This disclosure relates to an assembly for vibrating a compacting drum of a compacting machine, the assembly comprising a shaft rotatably mountable to a compacting drum of the compacting machine, the centre of mass of the shaft being offset from the geometrical rotation axis of the shaft, an outer eccentric member being arranged outside of the shaft, and the centre of mass of the outer eccentric member being offset from the geometrical rotation axis of the shaft, and the outer eccentric member being displaceably mounted relative to the shah for adjustment of the eccentricity of the assembly. The disclosure also relates to a compacting machine comprising a frame, at least one compacting drum rotatably connected to the frame, as well as the previously mentioned assembly being mounted to the compacting drum.
The disclosure relates to an assembly for vibrating a compacting machine for compaction of materials, in particular in earthwork and road construction. Document US20040182185A1 shows an adjusting device for regulating the eccentric moment of an eccentric shaft of a roller drum. The shown device shows an inner eccentric shaft being rotationally powered by a motor and an outer eccentric shaft being, rotatable relative to the inner eccentric shaft. The outer eccentric shaft comprises two axially spaced apart eccentric weights that may be used for variably adjusting the resulting total mass eccentricity of the assembly. Consequently, desired vibration amplitude may nearly always be selected from a relatively wide range of vibratory amplitudes.
A disadvantage of the solution of D1 is a relatively high power demand of the driving motor.
There is thus a need for an improved assembly for vibrating a compacting machine removing the above mentioned disadvantage.
It is desirable to provide an assembly for a compacting drum of a compacting machine, where the previously mentioned problem is at least partly avoided.
The disclosure concerns an assembly for vibrating a compacting drum of a compacting machine, the assembly comprising a shaft rotatably mountable to a compacting drum of the compacting machine, the centre of mass of the shaft being offset from the geometrical rotation axis of the shaft, and an outer eccentric member arranged outside of the shaft, the centre of mass of the outer eccentric, member being offset from the geometrical rotation axis of the shaft, and the outer eccentric member being displaceably mounted relative to the shaft for adjustment of the eccentricity of the assembly
The disclosure is characterized in an extension of the outer eccentric member in a direction parallel with the geometrical rotation axis of the shaft is at least two times an average extension of the outer eccentric member in a radial direction perpendicular to the geometrical rotation axis of shaft such that a mass of the outer eccentric member forms a distributed load along the geometrical rotation axis of the shaft.
The selected relationship between the axial extension of the outer eccentric member and the average extension of the outer eccentric member in a radial direction results in a certain level of axial mass distribution of the outer eccentric member. By distributing the mass of the outer eccentric member in the direction of the geometrical rotation axis of the shaft the assembly, also referred to as axial direction hereinafter, the moment of inertia of the outer eccentric member is reduced. This reduction in moment of inertia is the result of a reduced distance (D) between the geometrical rotation axis of the outer eccentric member and the centre of weight of the outer eccentric member in a plane perpendicular to the axial direction. The moment of inertia (I) of the outer eccentric member equals the product of the mass (M) and said distance (D) squared, i.e I=M×D2. Hence, by reducing the distance the moment of inertia is reduced. A reduced distance between the geometrical rotation axis of the outer eccentric member and the centre of weight of the outer eccentric member in a plane perpendicular to the axial direction naturally also results in reduced eccentricity of the outer eccentric, member, where the eccentricity is the product of the mass (M) and said distance (D). However, when for example doubling the mass (M) and reducing the distance (D) by half, the eccentricity has not changed but the moment of inertia is reduced due to the squared distance (D2) in the moment of inertia calculation. As a result, by distributing the mass of the outer eccentric member in the axial direction, the moment of inertia may be reduced while the eccentricity of the outer eccentric member is kept constant.
A reduced moment of inertia of the outer eccentric member results in a reduced moment of inertia of the complete assembly when nothing else has been changed, and this allows a reduced power output of the motor that is used for rotating the assembly while the rotational acceleration remains unchanged. A reduced power output demand of the motor allows a correspondingly smaller motor power, which consequently requires less power output of the main power source of the compacting machine. For example, a smaller hydraulic motor for powering the eccentric assembly allows a reduced hydraulic power output of the hydraulic pump driving the hydraulic motor. As a result, the main diesel engine powering the hydraulic pump may have a reduced maximal power output, and thus reduced fuel consumption. In all, the solution of the disclosure allows reduced fuel consumption.
Further advantages can be achieved. For example, the extension of the outer eccentric member in the direction parallel with the geometrical rotation axis of the shaft may be at least three times, preferably at least five times, and more preferably at least ten times the average extension of the outer eccentric member in the radial direction perpendicular to the geometrical rotation axis of the shaft. A more distributed load and a shorter radial distance between the load and the centre of rotation of the shaft results in further reduced moment of inertia.
The outer eccentric, member may have an extension in the direction parallel with the geometrical rotation axis of the shaft exceeding 10%, preferably exceeding 20%, and more preferably exceeding 50% of the unsupported length of the shaft. As described above, a more distributed load results in that the centre of mass of the eccentric member can be located closer to the rotational axis of the shaft, and thereby reducing the moment of inertia for a given mass.
The outer eccentric member may have an extension in the direction parallel with the geometrical rotation axis of the shaft exceeding 10%, preferably exceeding 20%, and more preferably exceeding 50% of the length of an eccentric mass of the shaft.
The outer eccentric member may exhibit an axial length of at least 100 millimeters, preferably at least 150 millimeters, and more preferably at least 200 millimeters. A distributed load of the eccentric member yield advantageous aspects in terms of energy efficiency.
The outer eccentric member may be pivotally mounted relative to the shaft. This arrangement enables a robust design and cost-effective manufacturing of the assembly.
The mass of any axial segment of an unsupported axial length of the outer eccentric member may differ less than 75% from the mass of any other axial segment of the unsupported axial length of the outer eccentric member with the same axial length, preferably less than 50%, and more preferably less than 40%. A more evenly distributed mass over the length of the eccentric member enables reduced moment of inertia of the eccentric member.
The mass of the unsupported axial length of the outer eccentric member is substantially regularly distributed over the unsupported axial length of the outer eccentric member. A more evenly distributed mass over the length of the eccentric member enables reduced moment of inertia of the eccentric member.
The outer eccentric member is attached to the shaft by means of at least two support members, said at least two support members being spaced apart in a direction of the geometrical rotation axis of the shaft and pivotally mounted on the exterior of the shaft. This arrangement enables a reliable and robust rotatable mounting of the outer eccentric member to the shaft. The rotatable mounting may be realised by relatively narrow roller or sliding bearings, thereby enabling low maintenance costs and high reliability.
Each support member may be formed as an individual member that connects the outer eccentric member with the shaft. This design enables cost-effective manufacturing.
One support member may be positioned on each side of an eccentric mass of the shaft. This layout enables a robust design.
The outer eccentric member is rotatable relative to the shaft in an angular range that is limited by a first end position at a first end of the range and a second end position at a second end of the range, which angular range is less than 360 degrees, preferably less than 180 degrees. 180 degrees appears to represent the largest possible difference in total assembly eccentricity between the first and second end positions, where the eccentricity of the shaft and the outer eccentric member match in one of said first or second end positions and are opposite each other in the other of said first or second end positions.
The total centre of mass of the shaft and the outer eccentric member is offset from the geometrical rotation axis of the shaft with a first distance when the outer eccentric member is located in a first end position, and the total centre of mass of the shaft and the outer eccentric member is offset from the geometrical rotation axis of the shaft with a second distance when the outer eccentric member is located in a second end position, wherein the first and second distances are different. This arrangement essentially implies that the assembly exhibits two different levels of eccentricity of the total assembly depending on the position of the outer eccentric member. This is advantageous when compacting different types of material and material layer thickness, wherein eccentricity oldie total assembly may be selected to best fit the specific situation.
The shaft may comprise a first stop arrangement for preventing relative rotation between the shaft and the outer eccentric member in a first angular direction at a first end position, and a second stop arrangement for preventing relative rotation between the shaft and the outer eccentric member in a second angular direction, opposite to the first angular direction, at the second end position. The first and second stop arrangements allow selection of the total assembly eccentricity simply by means of rotating the shaft in a first direction or a second direction. This arrangement enables a particularly robust and reliable design of a multi-position eccentric assembly because no moving control and/or actuating members are required to change the eccentricity of the assembly.
The assembly may comprise spring means for damping an impact force that may be generated when the outer eccentric member or the support members is/are brought into contact with the shaft at the first end position and/or the second end position. When the outer eccentric member is located in for example the first end position and the shaft suddenly is powered to rotate in the opposite direction, the outer eccentric member will change angular position relative to the shaft to the other end position. Depending on the acceleration of the shaft, the outer eccentric member will arrive at the other end position having angular speed that is different from the angular speed of the shaft, such that a sudden change in angular speed of the outer eccentric member will occur. The moment of inertia in combination with a sudden change in angular speed may result in a relatively high contact force between the outer eccentric member and the shaft, and this force must be absorbed without damaging the assembly. Previously, this was realised by forming the parts of the assembly relatively strong and robust such that the impact force could be absorbed without damages. However, strong and robust parts imply a high moment of inertia, which implies a relatively high power output of the motor for rotationally powering the assembly, thereby resulting in high fuel consumption of the compacting machine. By providing the assembly with spring means for clamping the impact force the parts of the assembly, in particular the shaft and the outer eccentric member may be less strong and robust, such that a reduced moment of inertia results, and thereby also reducing the fuel consumption.
The spring means may be arranged on the outer eccentric member, in particular at the end regions of the outer eccentric member. Alternatively, the spring means may be arranged on the shaft, in particular at the end regions of the shaft. Still alternatively, the spring means may be arranged on one or more of said at least two support members.
The spring means may comprise at least one spring member in form of helical spring, disc spring, elastic member, or the like.
The spring means itself may be arranged to directly contact the shaft and the outer eccentric member for absorbing impact energy upon impact. This arrangement corresponds to a relative simple and cost-effective solution. Alternatively, the spring means may additionally comprise at least one abutment member arranged to transfer the impact energy to the spring member. The abutment member may be arranged to prevent damages to the spring member, and/or simplifying guidance of the spring means for preventing the spring means from unwanted deformation.
The at least one abutment member may cooperate with guiding means for guiding the at least one abutment member along a path, wherein the guiding means preferably is formed of at least one recess in which the at least one abutment member is at least partly slidingly positioned. Guiding means of the abutment member may enable guidance of the spring means for preventing the spring means from unwanted deformation.
The at least one spring member may be installed in a preloaded state, i.e in a compressed state. This arrangement enables a higher damping force from the very beginning of the motion path upon impact, and prevents loose parts in the assembly. The preloaded spring member may also enable a preloaded mounting of the outer eccentric member within the support members.
The at least one recess may be a through-hole, a first abutment member may be arranged at a first end of the through-hole, a second abutment member may be arranged at a second end of the through-hole, and the spring member may be arranged between the first and second abutment member. This arrangement allows damping means being located on both sides of a member, such as the outer eccentric member of support member. Hence, a single recess and a single spring member may be used for realising damping means on both sides of the member, thereby reducing costs.
The spring means may be positioned in a central region of the outer eccentric member and/or the shaft. This arrangement results in less spring means, thereby reducing cost. For example, the outer eccentric member may be constituted by at least one leaf spring, and the shaft may comprise at least one abutment surface positioned in a central region of the shaft, and the leaf spring may be arranged to interact with the abutment surface for damping the impact force.
The outer eccentric member may be constituted by at least one leaf spring, and the shaft comprises at least one projecting abutment member positioned in a central region of the shaft, and the leaf spring is arranged to interact with the projecting abutment member for damping the impact force. This arrangement defines an alternative solution for damping the impact force.
The outer eccentric member lay be constituted by at least one metal bar that is fastened to the at least two support members. This arrangement enables a cost-effective solution.
The outer eccentric, member may be constituted by at least two metal bars that are inserted in a recess in at least two support members, and the at least two metal bars are fastened to each of the support members by means of spring means that presses apart the at least two metal bars, such that each of at least two metal bar abuts an opposing inner surface of the recess of the at least two support members. This arrangement enables a rattle-free and fast mounting of the outer eccentric member, thereby simplifying manufacturing of the assembly.
The shaft may over a majority of its axial extension have substantially a cross-sectional circular segment shape in a plane perpendicular to the geometrical rotation axis of the shaft, wherein the circular segment has a central angle of more than 90 degrees, and preferably more than 120 degrees. It has been found that the shaft is provided with a particularly low moment of inertia in combination with a high eccentricity when the shaft and outer eccentric member jointly exhibits a circular cross-sectional area in a plane perpendicular to the axial direction, wherein a periphery of the circle crosses the geometrical centre of rotation of the shaft.
A majority of the mass of the outer eccentric member in a first end position may be located inside a geometrical cross-sectional circle in a plane perpendicular to the geometrical rotation axis of the shaft, which circle has the same centre and same radius as the circular segment. As mentioned above, it has been found that the shaft is provided with a particularly low moment of inertia in combination with a high eccentricity when the shaft and outer eccentric member jointly exhibits a circular cross-sectional area in a plane perpendicular to the axial direction, wherein a periphery of the circle crosses the geometrical centre of rotation of the shaft.
The geometrical rotation axis of the shaft may be positioned within, on or outside a geometrical cross-sectional circle in a plane perpendicular to the geometrical rotation axis of the shaft, which circle has the same centre and same radius as the circular segment.
The geometrical cross-sectional circle extends within a distance from the geometrical rotation axis of the shaft, which distance is in the range of 0-50 millimeters, preferably 0-25 millimeters, and more preferably 0-10 millimeters. As mentioned above, it has been found that the shaft is provided with a particularly low moment of inertia in combination with a high eccentricity when the shaft and outer eccentric member jointly exhibits a circular cross-sectional area in a plane perpendicular to the axial direction, wherein a periphery of the circle crosses the geometrical centre of rotation of the shaft. However, also when the periphery of the circle is located relatively close to the centre of rotation a significant reduction in moment of inertia is achieved.
Each support member may be formed by a connecting rod. This enables a reduced moment of inertia.
The shaft may be a solid shaft. A solid shaft without an internal cavity enables a reduced moment of inertia of the assembly.
The disclosure also relates to a compacting machine that comprises a frame and at least one compacting drum according to the disclosure rotatably connected to the frame.
The compacting machine may further comprise a motor for rotationally driving the assembly in any rotational direction, wherein the assembly may be rotationally mounted in two spaced apart parallel supports that are fastened to an interior wall of the compacting drum, which supports are configured to transfer vibrations generated by the assembly to the compacting drum.